A slot antenna may be formed when a slot is formed in a conductive sheet (often referred to as a reference plane, and herein referred to as a “reference sheet”). The slot may be formed in the reference sheet by cutting or stamping the reference sheet, or by using a die casting that has features which result in producing a slotted reference sheet from molten material that is allowed to cool in the mold.
Usually, the length of the slot is selected to be half the wavelength of a signal that is produced at a desired frequency. The width of the slot is often a small fraction of the wavelength. The slot may take different shapes. For example, the slot may be a rectangle or a spiral. In the case of a spiral slot, the shape of the spiral slot is selected to provide a specific gain, bandwidth and return loss.
Since the current flow in a slot antenna is not confined to the edges of the slot, the current flows over the entire reference sheet making the antenna a very efficient radiator. This type of antenna normally radiates from both sides of the reference sheet equally. Prior art slot antennas typically take advantage of the radiation pattern from both sides of the reference sheet, or utilize wave guides as a means of directing the radiation emitted from the reference sheet.